This invention relates generally to gas turbine engines and more particularly to swirler arrangements for supplying combustion air to the combustor of such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In combustors used with aircraft engines, the fuel is typically supplied to the combustor through a fuel nozzle positioned at one end of the combustion zone, and air is supplied through a surrounding assembly, known as a swirler, which imparts a swirling motion to the air so as to cause the air and fuel to be thoroughly mixed.
Traditionally, two types of swirlers have been used. One type of swirler includes a plurality of circumferentially-spaced swirl vanes that produce the swirling motion of the air. In the other type, the swirler is provided with a plurality of angularly directed passages, commonly referred to as air jet holes, which cause the desired swirling of the air. The proper sizing of the air jet holes is important because the swirlers are required to provide a certain amount of airflow to achieve the correct fuel-to-air ratio. It is also common to provide swirlers with purge holes for the purpose of avoiding coking on structure adjacent to the swirler.
Conventional swirlers are often made through a process in which a casting of the swirler body is made, and then the air jet holes and any purge holes are formed by either a mechanical drilling and final reaming method or an electro-discharge machining method. While generally providing excellent results, these methods are relatively expensive and time consuming processes that consequently add cost to the manufacture of the swirlers. Accordingly, attempts have been made to produce swirlers as castings with as-cast holes to avoid the cost of these secondary machining processes. However, because the amount of airflow through these holes is affected by a number of hole parameters (i.e., the hole size, the hole angle, the inlet and exit geometry of the hole, and the interior surface finish of the hole), achieving equivalent airflow for an as-cast hole relative to a fully machined and finished hole has proven to be difficult.
Fabricating the necessary casting tooling for as-cast holes requires an iterative process in which a sacrificial swirler is cast with holes that are clearly oversized. These holes are flowchecked and the casting tool is modified to form a smaller hole. These steps are repeated, over and over again with progressively smaller holes, until the desired airflow is achieved. Many iterations are typically required to reach the desired airflow. Thus, developing the tooling for swirlers with as-cast holes is a time consuming and expensive process which must be gone through for every swirler design and every time a swirler design is changed.
Accordingly, there is a need for a method of making swirlers with as-cast holes, particularly determining the proper hole parameters to be used in the casting process, that is free of the above-mentioned problems.